1. Field of the Invention
The present invention relates to cannulas used in surgical applications, and more particularly, to systems used in guiding such cannulas to the surgical field within the body of a patient.
2. Description of Related Art
In medical applications and specifically in surgery, the list of uses for cannulas is exhaustive. One application involves the augmenting or supplementing of pulmonary blood flow through the beating heart during heart surgery by use of one or more cannulas involved in the intake and return of blood into the circulatory system. The cannulas interface between the patient's circulatory system and the mechanical pumps that power the augmentation process. Such an application is described in co-pending PCT Application No. PCT/US97/18674 entitled "Single Port Cardiac Support Apparatus", filed Oct. 14, 1997 and incorporated herein by reference in its entirety.
Typically, placement of the cannula at the desired location within the patient's body is facilitated by use of guiding devices such as a guide wire threaded through the cannula. The guide wire is easier to manipulate than the cannula, and its placement precedes placement of the cannula. After the guide wire is in place, the cannula is pushed along the length of the guide wire, following the guide wire to the desired destination.
It is also known that a balloon catheter can be used as a guide wire. Balloon catheters are well known in the art and have a multitude of uses, including delivery or removal of fluid from the surgical site. However, balloon catheters are typically at least an order of magnitude smaller than cannulas. Their small size accordingly severely limits their application since both quantity and rate of fluid flow through the catheter are limited. In fact it is precisely because of their small size that balloon catheters can be used as guiding devices for the larger, more robust and versatile cannulas. During use as a guiding device for a cannula, the balloon catheter acts as a guide wire in facilitating the advancement of the cannula to the desired destination. The balloon catheter is first inserted into a desired position within the patient's body, then the cannula is inserted over the balloon catheter, and then advanced into the desired position.
Insertion of the balloon catheter is effected using the inflatable balloon disposed at a distal tip of the balloon catheter. A lumen in communication with the balloon delivers inflating fluid to the balloon, thereby inflating the balloon and causing it to operate as a "sail" which is pulled along in the blood stream through the natural blood flow in the patient's circulatory system.
Further the cannula may be inserted within the patient's body without the aid of any external guiding means. However, this method may be unsatisfactory because the cannula may not be placed properly within the patent's body, thereby causing tissue damage.
Use of guiding devices in the placement of cannulas is particularly unsatisfactory because of the risk of injury to the delicate tissues, especially when the guiding device is withdrawn. The problem is particularly acute when the delicate aortic or pulmonary semilunar valves are involved, restricting the ability to cannulate some portions of the heart during cardiac surgery. Additionally, the process of inserting the guiding device prior to insertion of the cannula requires monitoring of the guiding device in its progress, typically using X-rays. Incident to X-ray use are inherent risks and constraints, and in emergency situations X-ray equipment may not be available at all, or its use may introduce prohibitive time delays.
Moreover, reliance on balloon catheters or other guiding devices for cannula placement introduces a series of additional steps to the cannulation procedure. Since time is critical during surgical applications and the need to minimize the chances of complications of paramount importance, there is a long felt need for a system in which cannulation is effected in a rapid and efficient manner.